UNSOLVED crimes are enough to send a shiver down your spine and the mystery of the Tylenol murders is no different.

It's been 26 years since seven people were killed after taking Tylenol capsules that were laced with potassium cyanide in Chicago, but despite the FBI recently reopening the case, there is still no answer as to who was behind the vicious crimes.

Twelve-year-old Mary Kellerman was the first to die in Chicago's unsolved Tylenol murders

The murders began in September 1982 when 12-year-old Chicago resident Mary Kellermen died after taking Tylenol capsules that had been poisoned.

Mary had woken up that morning with a cold and her parents gave her the painkiller to calm the symptoms, but just hours later she died.

Later that morning, in another Chicago suburb, postal worker Adam Janus collapsed and died too.

While mourning the death of their brother, Adam's brother Stanley and his sister-in-law Theresa both took painkillers from the same batch and soon died too.

Postal worker Adam Janus was the second victim of the Chicago Tylenol murders

Hours after Adam 27-year-old mum Mary Reiner, who had just given birth to her fourth child, felt unwell and took some tablets before collapsing and dying at home.

The same day, Mary McFarland, a 31-year-old shop worker told her colleagues she has a bad headache - she died

Stenographer Diane Elsroth, 23, was staying at her boyfriend's family home in New York when she took a headache pill and went to bed. She was found dead the following day.

The death toll was now at seven and the only link between each of the victims was that they'd all taken Extra-Strength Tylenol before they died.

Adam's sister-in-law Theresa Janus also fell victim to the pills

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When the pills were tested, they were found to contain such a high level of potassium cyanide that they were toxic enough to cause thousands of deaths.

But other than this information, the police were stumped about suspects or motives behind the killings.

The pills had all been made in different production plants and were sold in different pharmacies throughout the Chicago area, without there seeming to be any pattern.

The investigators seemed to think that the culprit had been tampering with the pills while they sat on the shelves of each store.

Adam's brother Stanley was one of the three family members to be murdered

The deaths set off nationwide hysteria and bottles of Tylenol medication were removed from shops and worried consumers flooded hospitals and poison control helplines with panicked questions.

Police went as far as driving down Chicago's streets warning people against taking Tylenol through loudspeakers while the company who made the pills, Johnson & Johnson, lost millions of dollars calling back all the bottles from pharmacies across the country.

Unfortunately, the Tylenol murders prompted copy cats across the country.

So much so that The Food and Drug Administration in America counted up over 270 different cases of people tampering with products in the month following the murders.

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Diane Elsroth was a victim of the poisonings at the age of 23

People were treated for everything from rat poison tainted pills to hydrochloric acid poisoning across the US and, that Halloween, parents even reported finding sharp pins inside their kids' Halloween treats.

Only one man was ever a suspect in the Tylenol murders.

James Lewis, a tax consultant, penned a letter to Johnson & Johnson in 1982 demanding $1 million in return to "stop the killings."

Lewis had actually already been charged with a murder four years earlier in 1978 when police found the remains of one of his customers in bags in his attics.

Mary Reiner was killed shortly after having her fourth child

However, the charges were later dropped when a judge ruled that the search of Lewis' house was illegal.

Police also struggled to connect Lewis to the Tylenol killings and Lewis denied committing them, but he was convicted of extortion for the letter and ended up spending over 12 years in federal prison.

The Chicago police superintendent, Richard Brzeczek, later said that he doubted Lewis would ever actually be prosecuted for the murders.

In 2009 the FBI reopened the investigation into the Tylenol murders and even focused their investigation on Lewis.

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Johnson & Johnson, the makers of Tylenol, lost millions recalling bottles of the pills after seven people died

Despite not naming him as the focus, the FBI have since conducted searches of his storage unit and office.

Since the murders, product safety standards in the US were dramatically improved - with packaging being improved and tamper proof seals being added to products.

But whether or not the crimes will ever be solved, and who was behind them, remains a mystery.